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J. Micromech. Microeng. 6 (1996) 410425. Printed in the UK

Micromechanical engineering: a basis

for the low-cost manufacturing of

mechanical microdevices using

microequipment

Ernst M Kussul, Dmitri A Rachkovskij, Tatyana N Baidyk andSemion A Talayev

Institute of Cybernetics, National Ukrainian Academy of Sciences, ProspectGlushkova 40, Kiev 252187, Ukraine

Received 24 July 1996, accepted for publication 15 August 1996

Abstract. Microelectronics-based micromechanics is rather limited for theconstruction of 3D micromechanisms with moving parts. We propose to use

microequipment to transfer the technologies of mechanical engineering to themicrodomain. We show that equipment precision increases linearly with decreasingsize. To make microequipment, we suggest a series of equipment generations withgradually decreasing dimensions. Miniaturization of equipment will reduce powerconsumption and floor area occupied. Coupled with automation, it will drasticallyreduce the cost of microequipment. This in its turn will reduce the cost ofmicromechanical devices manufactured by microequipment. Microequipment-basedmanufacturing will also increase throughput by the concurrent operation of largenumbers of low-cost microequipment pieces. The low cost and high productivity ofmicroequipment-based manufacturing will widen the range of feasiblemicromechanical applications, both single-unit and mass. We propose designs formicrovalve fluid filters, capillary heat exchangers, electromagnetic and hydraulicstep motors that could be easily implemented by micromechanical engineeringtechnologies. Hybrid technologies combining massively parallel microequipmentbased manufacturing and batch manufacturing may also be promising.

1. Introduction

Nowadays, technologies for the microminiaturization

of mechanical structures are being developed within

the fields that are commonly referred to as micro

electro mechanical systems (MEMS) in the USA [1, 2],

micro system technology (MST) in Europe [3] and

micromachine technology in Japan [4, 5]. The substantial

part of all these technologies is integrated circuit (IC)

based batch technologies from microelectronics [6,7].

Microelectronics-based technologies enable the creation

of microdevices that incorporate simple mechanical

components [8, 9] fabricated mainly from silicon [10].The development of complex microsystems such as

miniature machine tools, manipulators and robots [11, 12]

calls for the development of sophisticated mechanical

structures that have 3D movable and complex-shaped parts

made from diverse materials. This spurred on work on

the modification of existing technologies [7] as well as the

development of novel technologies [13] to meet the needs

of micromechanics.

A number of technologies which emerged in microme-

chanics as a result of this work (LIGA [14, 15], surface mi-

cromachining [16, 17], anodic bonding [18, 19], etc) belong

to the category of batch processes as well as their parent

microelectronics technologies. Others belong to the cate-

gory of individual processes (e.g., micro stereo lithography

[20, 21], laser micromachining [22, 23], micro-EDM [24],

microgrinding [25], and other technologies [26] originated

in mechanical engineering).

The need for individual processing is caused by the

restriction of materials, the shape of parts, and structures

inherent in batch processing [27,5, 13]. Individual

processing is a basis for mechanical engineering, where

there is already a wealth of experience in the design

and fabrication of sophisticated machines and mechanismsincluding 3D structures and movable parts.

The use of mechanical engineering technologies to

make micro machinery [2833] raises a number of issues

that are still unclear. These issues concern the limits

of mechanical machining, ways of achieving them, the

cost and throughput of equipment, and the range and

cost of potential applications. Some aspects of these are

discussed in this paper. In section 2 we consider the

typical features of both batch and individual processes.

The dimensional limits of various mechanical machining

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Micromechanical engineering and microequipment

methods are estimated in section 3. In section 4 we

examine various errors that influence the precision of

machine tools and show that the equipment precision

increases linearly with decreasing in size. In section 5

we propose to make microequipment by using generations

of smaller and smaller machine tools. In section 6

we introduce the notion of micromechanical engineering

and show that microequipment allows reduction of the

unit cost of operation and increases the throughput

by the massive parallelization of manufacturing. Theclassification of micromechanical applications as well as

examples of microdevices we are developing are presented

in section 7. A comparison between micromechanical

engineering and microelectronics-based micromechanics is

made in section 8. Discussion and conclusion are given in

sections 9 and 10 respectively.

2. Individual versus batch processes

We interpret a batch process as a process wherein common

machining or assembling operations are simultaneously

performed on the whole batch of workpieces through a

distributed chemical or physical action (figure 1).Examples of batch processes provided by microelec-

tronic technologies include photolithography, spin coating,

etching, diffusion of dopants, implantation, epitaxy, chemi-

cal vapor deposition, film technology, etc, as well as LIGA,

surface micromachining and anodic bonding. Workpieces

are silicon, GaAs, glass, ceramics wafers, possibly with lay-

ers of other materials formed on their surfaces, copper-clad

glass-cloth laminate for printed-circuit boards and printed-

circuit boards with inserted components prepared for solder-

ing. Operations include light exposing, etching, deposition,

bonding, wave soldering, casting and electroforming.

Under an individual process, each machining or

assembling operation is performed on a single workpiece

(figure 2). Examples of individual processes are provided

by turning, grinding, milling, drilling, broaching, forging,

EDM and stereo lithography.

There are technologies that are widely used in both

batch and individual processing. Casting, molding,

polishing and electrochemical machining are examples.

The necessity of individual processes is dictated by the

fact that batch processes possessing such merits as low

cost, high quality, high throughput in mass production, also

have a number of restrictions due to the peculiarities of

their implementation. Some batch processes can be used

only with certain materials. For example, high temperature

diffusion (e.g., oxide film manufacture, diffusion doping,

bonding) cannot be used with materials that have lowmelting or decomposition temperatures.

One of the main restrictions of batch processes is that

they result basically in planar 2D or 2.5D [5] parts, that

is, parts with constant cross-sections along some direction.

This restriction is caused by the following peculiarities of

batch processes.

For a number of batch operations, the distributed

working action (e.g., polishing, exposure, etching or

deposition) is modulated in the plane by 2D masks. Batch

relative alignment of the mask and each workpiece is

Figure 1. Examples of batch processes. (a) Working:exposure, development, etching. (b) Bonding. (c) Results.

practically achieved by a rigid fixation of each workpiece to

the 2D planar rigid base (e.g., handle wafer or board) and

alignment of the entire base. Distributed working action

on stationary workpieces modulated by 2D projection or

contact masks results in 2D fabricated parts. Fabrication

of true complex 3D parts by batch processes requires a

sequential build up of planar 2D layers. It prolongs the

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Figure 2. Examples of individual processes. Working: (a)turning, (b) drilling, (c) beam processing. (d) Assembly. (e)Result.

process and causes problems in obtaining quality bonding

of adjacent layers.

Fabrication of 3D structures from 2D parts is very

difficult. This is demonstrated by the fact that commercial

3D ICs are not yet available. For micromechanical

structures, especially with movable parts, this task is

complicated by the constraints imposed by batch assembly

techniques [5, 34] and by limited expertise in the design of

essentially 3D structures from 2D components. Practically,

micromechanical devices are often more the result ofavailable batch fabrication technologies rather than optimal

design.

Feedback control of batch processes is also limited.

Since the working action is directed upon the whole batch,

it can be controlled by feedback from a representative

workpiece, but not from each workpiece of the batch. To

get identical processing results for each workpiece, the

uniformity of working action, environment, and workpiece

properties should be ensured for the whole batch.

Therefore the peculiarities of batch processing impose

severe requirements on the tolerances of process parameters

at all stages of batch production. This, in turn, necessitates

equipment of increasing complexity and cost, includingclean rooms, as well as the high cost of production set-up,

leading to economical inefficiency of single-unit or small-

lot production by batch processes.

In traditional mechanical engineering there is vast

experience of the design and fabrication of 3D machines

and mechanisms with movable parts from various

materials. Individual machining and assembly are typical

of mechanical engineering production.

In individual processing, each operation is performed

on a sole workpiece. This enables the use of not only

distributed, but also spatially localized working action (e.g.,

working tool) and the ability to move the working tool

and the workpiece arbitrarily in space. Together with the

diversity of processing means, this permits the manufacture

of parts of complex 3D shape from virtually any material.

The possibility of true feedback control over the

individual machining of each workpiece allows tolerable

deviation of process parameters. Unlike batch processes,

individual processes are compatible with intermediate

quality inspection operations, which are inherently

individual.

The advantage of individual processes over the batch

ones is most conspicuous in assembly. Alignment of

components for batch assembly demands a special accuracy

of their positioning on the handle base because each

component is rigidly fixed on the base and its position

cannot be adjusted during assembly. For individualassembly, the adjustment of component position is possible.

Assembling often requires a sequence of movements that

are difficult to implement with the spatial fixation of parts

typical for batch processes. For example, rocking and

rotation of a shaft is needed to insert it into a hole with

small clearance. Again, assembly by bonding limits the

implementation of movable joints.

The drawbacks of individual processes are a lower

throughputcost ratio for equipment and a higher processing

cost per work item compared to those of batch processes.

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Table 1. Typical features of batch and individual processes.

Batch process Individual process

Number of workpieces Large OneProcessing action Distributed LocalProcessing agent Liquid or gas ToolSpectrum of materials Limited BroadWorkpiece fastening Rigid Movable3D capabilities Limited ArbitraryAssembly Bonding JoiningJoints Unmovable MovableStructures Simple monolithic Complex movableFeedback control Averaged IndividualQuality inspection Partial FullProcess tolerances Stringent RelaxedSet-up Complicated ModerateCost of processing Low HighProcessing throughput Low High

3.1.2. Removal of material using an electric field.

Micro-EDM and electrochemical removal and deposition

fall into this category.

Micromachining by micro-EDM is well-known [24]

and has been used to machine shafts and holes with 5 diameter, radial deviation of less than 0.5 , and surface

roughness less than 0.1 [13]. Micronozzles of 2.3

diameter were also reported [42]. The limits of EDM can

reach atomic dimensions, because its operation principle

does not differ from that of STM, single atoms can be

removed [43, 44]. The drawbacks of EDM are relatively

low productivity and restriction of materials.

Electrochemical etching and deposition have reached

submicron range [45] and allow the fabrication of 3D

structures [46]. Though electrochemical processing deals

in principle with the removal and the deposition of discrete

atoms, the statistical nature of chemical reactions prevents

reaching atomic order accuracy.

3.2. Machining by redistribution of material

Redistribution of material is accomplished by high pressure,

at various temperatures and aggregate states of ductile

materials.

3.2.1. Unrestricted redistribution. Free forging

(hammering) and diamond burnishing fall into this

category. Among the machining methods considered in

this paper, these two are potentially the most precise.

If the machining material is ductile enough, unrestricted

deformation should allow the achievement of surfaceroughnesses of the order of crystal lattice spacing, through

local action on the individual atoms or molecules similar

to the operation of atomic force microscopes (AFM) [47].

Diamond burnishing may result in a surface finish better

than that obtained with diamond turning [41].

3.2.2. Restricted deformation. Relevant techniques

include die forging (pressing), casting and molding.

Dimensional accuracy of parts produced is determined

by the surface roughness, shape complexity and accuracy of

die or mold, by the plasticity of material, and by distortions

during removal of ready parts. Additional errors appear

after the removal of ready parts as a result of cooling

deformations.

Errors owing to cooling deformations should scale

down linearly with the size of parts produced. Errors owing

to die or molding filling and removal do not change with

downsizing of parts produced. Microdie fabrication errors

are determined in a manner similar to the fabrication errors

of any other micromechanical devices. Metal casting errors

include those due to crystallization.

Thus, the total error for machining by restricted

deformation results from several sources and exceeds the

error of other techniques discussed above. The size error

is still more than 1 , and the surface roughness is more

than 0.1 (see [3], p 44). However this type of machining

provides high throughput and can be used for fabrication

of workpieces and parts that do not require high accuracy.

3.2.3. Semi-restricted deformation. Examples are

rolling and drawing. The deformation takes place in 1D

(drawing and some kinds of rolling) or in 2D (plate or

foil rolling). Accuracy of these techniques is intermediate

between unrestricted and restricted deformation, and is

determined by the accuracy of fabrication and positioning of

equipment (roller or die). Surface roughness is determined

by that of the equipment and may approach the atomic

lattice spacing for simple shapes (foil rolling).

10 diameter tungsten wire with a radial deviation of

less than 0.1 has been manufactured [48] as has rolled

foil 2 thick [49].

To summarize, shape accuracy of 0.1 and average

surface roughness of 0.005 have been realized

by individual mechanical machining. The limits of

dimensional error are determined by the parameters and

structure of the crystal lattice of the material processed. To

reach the limits, equipment with the appropriate precision is

needed. Equipment precision is discussed in the following

section.

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4. Enhancement of equipment precision due to

downsizing

In this section we consider the key factors that influence

the accuracy of equipment. The key sources of machining

errors are heat expansion, geometry errors, clearances, lack

of machine tool rigidity, and feed step [50].

Let us compare various kinds of error for two machine

tools that are identical in design, material and relative

precision, but machine tool A and its workpiece are Stimes bigger than machine tool B and its workpiece in linear

dimension.

(i) Thermal expansion Since thermal expansion is

proportional to linear dimension, the thermal expansion of

machine tool B is Stimes less than that of machine tool A.

Thus, the machining error owing to thermal expansion will

be Stimes smaller for machine tool B than for A.

(ii) Geometry errors Due to the geometrical similarity

of machine tools A and B, the linear deviation of the

machine tool parts from their reference shapes are Stimes

smaller for machine tool B than for machine tool A. Thus

the machining error from this error source will be Stimes

smaller for machine tool B than for A.(iii) Clearances Due to geometrical similarity, the

smaller machine tool B has clearances Stimes smaller than

the larger machine tool A. Thus the error in workpiece

machining owing to clearances will be Stimes smaller for

machine tool B.

(iv) Lack of rigidity The rigidity of a machine tool is

proportional to the ratio between the force acting on a part

of the machine tool and its displacement due to deformation

caused by the force. Since the rigidity of geometrically

similar objects decreases linearly with size [51], the rigidity

of machine tool B is Stimes less than that of A.

The error of workpiece machining due to the lack of

rigidity of a machine tool depends on the displacement of

its elements under the action of various forces. To estimate

these displacements, one must analyse how various forces

acting on the machine tool parts depend on of the machine

tool size.

Let us consider the cutting force, assuming that the

feed and the cut depth of machine tool B are Stimes less

than those of A. Since the cutting force is approximately

proportional to the cross section of chips [52], the cutting

force of machine tool B is S2 times less than that of A.

Since the rigidity of B is Stimes less, the displacement of

the parts of B due to the cutting force will be Stimes less

than those of A.

Another force responsible for displacement of machine

tool parts is inertial force due to vibration. Since inertialforce is proportional to the masses of machine tool parts,

the inertial force for B is S3 times less than that for A.

Therefore the displacement due to this force for B is S2

times less than those for A.

Thus machining error due to lack of rigidity will be at

least Stimes smaller for B than for A.

(v) Feed step Determined by the machine tool design,

the minimal feeding step of machine tool B is Stimes less

than that of A. Thus the machining error will be Stimes

smaller for B than for A.

Table 2. Linear dimensions of equipment generations.

Generation Generation downsizing factorG GDF = 2 GDF = 4 GDF = 8

1 100 mm 100 mm 100 mm2 50 mm 25 mm 12.5 mm3 25 mm 6 mm 1.5 mm4 12.5 mm 1.5 mm 0.2 mm5 6 mm 0.4 mm 25 6 3 mm 0.1 mm 3 7 1.5 mm 25 8 0.8 mm 6 9 0.4 mm 1.5

10 0.2 mm

To summarize, since the absolute error from each error

source is at least Stimes smaller for B than for A, the

total absolute error of B will be at least Stimes smaller

than that of A. Thus, equipment accuracy increases linearly

with decreasing equipment size, and its relative precision

remains constant. Therefore we conclude that to avoid

problems of making ultraprecision macroequipment, it is

expedient to fabricate microparts using microequipmentwith dimensions commensurable with those of machined

parts (see also [33, 27]).

5. Making microequipment through smaller and

smaller generations

To make mechanical microequipment, we propose to use

the following scheme [53]. Equipment should be developed

as a sequence of generations. Each generation should

include equipment (machine tools, manipulators, assembly

devices, measuring instruments, tools, etc) sufficient for

the manufacture of an identical set of equipment. Each

subsequent equipment generation is manufactured by the

preceding one. The size of each subsequent generation is

less than that of the preceding generation.

First-generation microequipment should be manufac-

tured using macroequipment. Second-generation equipment

should be made using first-generation equipment, having

the same nomenclature but smaller dimensions than the first

generation. By realizing a series of smaller and smaller gen-

erations, equipment down to very small dimensions could

be obtained.

For example, if the dimensions of first-generation

machine tools were 100 mm 100 mm 100 mm, and

each subsequent generation was 444 times smaller than

the preceding one, then machine tools of the 9th generation

would have dimensions of approximately 1.5 1.5 1.5 . Let us define the generation downsizing factor

(GDF) as the ratio of the linear dimension of the preceding

generation equipment to that of the subsequent generation

equipment. For the example above, GDF is equal to 4

(GDF = 4).

The linear dimensions of equipment of sequential

generations (G) for various GDF and a 100 mm first

generation are shown in table 2.

To implement this scheme, equipment should permit the

fabrication of GDF-times smaller copies of its parts, while

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preserving their relative accuracy, therefore reducing their

absolute value by the GDF factor. Thus the geometrical

similarity of machine tools of various generations, and

therefore their relative precision (section 4) will be

preserved.

In mechanical engineering a number of techniques are

used to enhance the accuracy of equipment [5456]:

(i) Design solutions have been developed for some

machining operations that prevent transferral of equipmentparts error into machined parts error. For example,

the shape error of a part machined by turning may be

considerably smaller than that of the lathes slides or

spindle.

(ii) Many finishing operations have been developed

with the working principle of providing independence of

the parts shape error from the error of the equipment.

Examples are lapping of mating surfaces (cones, screw

pairs, gear teeth, etc), final grinding of balls, and honing.

(iii) For CNC machine tools, machining accuracy

is being enhanced by controlling the drive using tables

to correct any machine tool inaccuracies or using

feedback from instruments measuring the size of machined

workpieces precisely.

Methods for equipment accuracy enhancement are used,

e.g., in the machine tool industry for the fabrication

of precision parts for ultraprecision machine tools. In

our scheme, with gradually decreasing equipment size,

the requirement for relative accuracy of machine tools

needed for the fabrication of geometrically similar parts

for the following generation of machine tools decreases

proportionally to GDF.

Note that the direct fabrication of mechanical

microequipment by existing ultraprecision mechanical

macroequipment does not allow the creation of machine

tools smaller than 1 mm3. Therefore, today, the

way to manufacture very small machine tools isseen through a sequence of mechanical microequipment

generations. The advantages of this approach consist

also in a gradual revelation of problems that arise in

the course of miniaturization [5,27, 57, 58]. Furthermore,

microequipment developed using this approach will span

the entire range of mechanical micromachining.

6. Microequipment-based manufacturing in

micromechanical engineering

Our approach to the manufacturing of mechanical

microdevices is based on the extension of mechanical

engineering technologies to the microdomain by a gradualminiaturization of equipment. Therefore it may be named

micromechanical engineering (MME), and manufacturing

using microequipment may be named microequipment-

based manufacturing (MbM).

Individual processes (figure 4(a)), such as mechanical

machining, are of major importance for mechanical

engineering. There exists an opinion that individual

processing is of high cost and low throughput compared

with batch processing. It is based on the comparison

of microelectronical and macromechanical manufacturing

Figure 4. (a) Individual, (b) batch, (c) massively parallelmanufacturing.

processes. The costs of macroequipment, labor, floor

area, and energy are assumed to be comparable for batch

and individual processes. However batch processing

(figure 4(b)) works entire batches of workpieces at once,

so its throughput is higher and working cost per unit is

lower than those of individual processing.

The situation reverses for MbM for to the following

reasons:

(i) Miniaturization of equipment leads to decreased

floor area occupied and energy consumed, and, therefore,decreases associated costs.

(ii) The labor costs are bound to decrease due to

the reduction of maintenance costs and a higher level of

automation expected in MbM.

(iii) Miniaturization of equipment by MbM results in

decreased costs. This is because microequipment itself

becomes the object of MbM. The realization of universal

microequipment capable of extended reproduction of itself

will allow the manufacture of low-cost microequipment in

a few reproductive acts because of the low consumption of

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materials, energy, labor, and floor area in MbM.

Thus the miniaturization of equipment opens the way to

a drastic decrease in the unit cost of individual processing.

At a low unit cost of individual micromachining, the most

natural way to achieve high throughput is to parallelize the

process of individual machining by concurrent use of a great

quantity of microequipment of the same kind (figure 4(c)).

This type of high-throughput process may be called

massively parallel to stress the difference from massmanufacturing in macromechanics and microelectronics. In

microelectronics, mass manufacturing is achieved not by

individual, but by batch processes. In macromechanics, the

high cost of macroequipment, the large floor area that it

occupies, and the high energy consumption prevents mass

parallelization of manufacturing. The number of machine

tools that concurrently mass produce identical parts in the

factory does not usually exceed several dozen.

Contrastingly, for a 1 dm3 microfactory exploiting

massively parallel MbM, the number of machine tools with

overall dimensions of 1.5 mm 1.5 mm 1.5 mm (e.g.,

GDF = 4, G = 4 in table 2) placed 3.5 mm apart (at 5 mm

intervals) will be 8000. Realization of machine tools with

smaller linear dimension, e.g., 0.1 mm (GDF = 4, G = 6),will make it possible to place 8 000000 machine tools in

a 1 dm3 factory. Thus, massively parallel MbM presumes

thousands and millions of concurrently performed identical

individual operations instead of single or dozens of such

operations in mass macromechanical production.

Exploitation of such a great number of microsized

machine tools is only feasible if they are automatically

operated and the microfactory as a whole is highly

automated. We expect that many useful and proven

concepts, ideas and techniques of automation can be

borrowed from mechanical engineering. They vary from

the principles of factory automation (FMS and CAM) to

the ideas of unified containers and clamping devices andtechniques of numerical control. However automation

of micromanufacturing has peculiarities that will require

special development. These will be discussed elsewhere

([59], see also section 9).

To summarize, massively parallel MbM should be

based on individual machining of microparts and assembly

of microdevices realized by parallel operation of a great

number of automated microequipment. This enables high

productivity and low unit costs, as for batch manufacturing.

Unlike batch processes, there are no problems with

fabrication of 3D parts and assembly of sophisticated

constructions. These features of massively parallel MbM

allow revision of the wide-spread belief about poor cost-

effectiveness of micromechanical production and individual

processes and allow the search for new areas of prospective

micromechanical applications.

7. Applications

The fabrication method proposed for micromechanical

devices will allow a broadening of the spectrum of potential

applications, due to an extension the spectrum of materials,

machining, assembly methods, and designs introduced

into micromechanics by micromechanical engineering.

The low cost of individual micromechanical machining

and assembly will make feasible a number of potential

applications as well as allowing development of novel

applications that are not at present considered economical.

This concerns both mass and small-lot applications.

Mass applications should be manufactured by massively

parallel MbM. However, unlike batch production where

mass manufacturing is an essential prerequisite to

economically attractive applications, because of the need tojustify the initial costs of equipment and production setting-

up, the mass of microapplication is not as critical for MbM.

With the availability of low-cost universal microequipment

(to be produced by mass and automated micromachine tool

industry) and reasonable labor expenditure, the making

of inexpensive single-unit and small-lot applications is

possible. This is especially important for research and

prototype manufacture, as well as for the fabrication of

unique microdevices that may have a market even at

relatively high cost.

7.1. Classification of micromechanical applications

Let us consider three types of micromechanical applications

distinguished by their function.

7.1.1. Applications oriented to the macroworld. There

are applications ([3, 30,60] and references therein) in

which micromechanical devices exert influence on the

macroworld. In these applications macroeffect is obtained

by the integration into a single structure of a vast number

of microparts, each performing a microfunction. Such

applications require supermass production and assembly

of parts at low cost. Examples are filters (see

subsection 7.3.1), heat exchangers (see subsection 7.3.2),

panels, tactile displays, supercapacitors and systems for the

separation and purification of liquids.With existing micromechanical technologies, some of

these applications are too expensive or difficult to realize.

Massively parallel MbM will allow the manufacture of

low-cost devices of this type because of its capability to

manufacture low-cost arbitrary shaped parts and make use

of any material, low-cost assembly and mass production.

7.1.2. Applications oriented to the microworld.

The diversity of materials required, the need to make

parts of complex shape and the need to assemble

sophisticated structures with movable joints prevents

complete fabrication of these applications exclusively by

batch technologies. For example, it is not practical toproduce microequipment by batch technologies.

By their complexity, potential and current applications

of this kind vary from mechanical microtools to microrobots

and include ([3,8, 9,6063] and references therein)

microsurgery instruments; microsensors; applications

in microelectronics (microconnectors, packaging, etc);

micromotors (see subsections 7.3.3 and 7.3.4) and

microactuators; microinstruments (including STM and

AFM); microsystems for drug delivery; microfluid analysis

system; bio micromanipulation (including cell handling);

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Table 3. Design characteristics of valve filters for fluids.

Valve diameter (mm) 1.0 0.2 0.02

Valve number ( 1000) 50 50 12 000Clearance () 5 1 0.1Performance (liter per second) 0.6 0.005 0.001Differential pressure (Pa) 10000 10000 10000Filter diameter (mm) 80 16 10Filter height (mm) 60 12 10

micromachine tools and micromanipulators; microrobots

(e.g. MITIs ); microfactories; etc.

7.1.3. Applications performing size-independent

functions. Into this category we place applications

related to storage and processing of information ([3], see

p 164, [57], and references therein). The application

of micromechanics to this area is directed both to the

miniaturization of available information storage devices

and to the development of novel information processing

devices. Miniaturization of existing systems for recording,storage, and playback of information, such as magnetic

disk drives, magnetic tape drives, and optical disk drives,

will enable enhancement of unit capacity and reduction

of power consumption and cost. Development of novel

types of devices for information storage and processing

may turn out to be promising from the standpoint of

their miniaturization potential, which may exceed that

of electronic devices. Examples of such devices are

microhydromechanical automata, memory and computers

[64].

7.2. Applications of micromechanical engineering

under development

7.2.1. Microvalve fluid filter. The basic idea of the

filter proposed lies in the formation of filter capillaries

so the pathway traversed by the fluid within the capillary

is as short as possible. This permits a reduction of

differential pressure and improves flushing of clogged

filters compared to other mechanical filter types ([60] and

references therein).

(i) Design The microvalve filter contains a huge number

of valve cells. A valve cell is shown in figure 5(a). It

consists of conic valve placed in a hole. Special protrusions

at the top of the hole hold the valve so there is a thin

clearance between the conic part of the valve and thehole walls. Fluid passes through this clearance, but solid

particles larger than the clearance cant pass. Fluid flow is

directed from the top to the bottom of the valve cell, so the

solid particle cake is collected at the top of the valve cell

and can be removed by back flow of gas or liquid.

A large number of valve cells are placed on the

microvalve filter plate (figure 5(b)). A number of these

plates are placed in the microvalve filter case (figure 5(c)).

Examples of the rated characteristics of water filters are

given in table 3.

Figure 5. Valve filter for fluids. (a) Valve cell, (b) filterplate, (c) macrocell.

(ii) Implementation In this filter only one part, namely

the conic valve, is to be made in mass volume. Holes in

the plates have to be made for the valves, and assembly

consists of one mass operation of setting the valves into

the holes. Thus, only three types of mass operations are

necessary for the manufacturing of this filter. The numberof other operations (manufacturing of plates and a filter

case, and the assembly of the whole filter after the plates are

filled with the valves) is small compared with the number

of mass operations mentioned above. Conic valves can

be manufactured by turning or rolling; other parts can

be manufactured by turning and drilling, assembly can be

realized by a 3 DOF manipulator.

Thus this filter design will provide high performance,

low overall dimensions, low differential pressure and is well

suited for production by massively parallel MbM.

7.2.2. Capillary heat exchanger. Micromechanics

allows to enhance performance of heat exchangers through

the increase of the ratio of the heat exchange surface to the

volume of the device.

(i) Design A capillary heat exchanger (CHEX) includes

a huge number of cells. A CHEX cell is shown in

figure 6(a). It contains a large number of short orthogonal

capillary slots that pass hot fluid in one direction and cold

fluid in another (perpendicular) direction. Parallel short

slots allows for a high flow rate and a small differential

pressure, and their small width allows rapid heat transfer

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Figure 6. (a) Capillary heat exchanger cell. (b) CHEX cellwith covers; (c) CHEX macrocell.

when the fluid passes the capillary. The capillaries are

separated by the plates. A CHEX cell has special covers,

as shown in figure 6(b), that permit arrangement of CHEX

cells in a matrix structure, shown in figure 6(c).

Hot fluid is input at the top of the matrix, passes through

the cells, and is also output at the top of matrix. Cold

fluid is input and output at the bottom of the matrix, also

Figure 7. Electromagnetic step motor.

traversing the cells. The matrix is constructed so the cross

section of inlet and outlet canals is large enough to ensure

a small pressure drop across them. A large number of

such matrices may be arranged in a larger matrix structure

(second-order structure) and so on.

(ii) Implementation Plates and cover plates can be

machined by milling; the openings in the matrix can be

machined by drilling. For assembly, separating plates

are placed on the bottom cover plate and covered by the

top cover plate. All plates are bonded by adhesive orsoldering. Assembled CHEX cells are placed into the

matrix openings and sealed by adhesive or soldering. All

assembly operations can be carried out by an automatic

manipulator.

This design will permit reduction of differential fluid

pressure inside the heat exchanger owing to decreasing

length of capillaries involved in heat exchange.

7.2.3. Electromagnetic step motor. Various microme-

chanical applications may demand motors of various types:

electrostatic, electromagnetic, piezo, etc [57, 58,65, 66].

Electrostatic motors may have a very simple design. The

dimensions of their parts are not much less than the over-all motor dimensions, making miniaturization easier. Their

drawback consists in a lower torque (in the micro version)

compared to other motors.

Electromagnetic motors may provide considerable

torque, but are more sensitive to the relative errors of

fabrication (gaps), and the minimal linear dimension of

their parts (wire diameter) is generally two orders less

than the overall motor dimensions, resulting in impaired

miniaturization potential. Our intent was to simplify the

design, fabrication, and miniaturization of electromagnetic

motor development.

(i) Design Our electromagnetic step motor (figure 7)

contains four coils fitted on steel cores. Steel cores are

fastened on a steel plate and on a non-magnetic plate. Theends of the steel cores are equipped with steel shoes to

provide a closed magnetic circuit. The rotor consists of

an axis and a permanent magnet fitted securely to this axis

(e.g., by adhesive). Opposing coil windings are connected

with each other, and to the electronic circuit for pulse

formation. By passing the current in the proper direction

through the appropriate coil pairs, one can control the rotor

position (total of 8 stable rotor positions).

(ii) Implementation The steel cores, steel plate, non-

magnetic plate, shaft, and rotor can be machined by turning.

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Table 4. The typical features of microelectronics-based and mechanical engineering based micromechanics.

Microelectronics-based Mechanical engineeringmicromechanics based micromechanics

Working techniques Batch Individual or batchBasic materials in use Silicon-based, some metals and polymers Metals, alloys, polymers and ceramicsComponent geometry Planar, 2.5D Complex, 3DAssembly methods None or bonding Joining, bondingPossible designs Planar or stack devices Machines with moving partsEquipment precision enhancement By equipment design By equipment downsizingBasic type of process control Feedforward FeedbackQuality inspection Final Final and intermediateQuality control By process tolerances By inspection and replacementAutomation methods Conventional To be refinedEquipment size Macro MicroProduction volume High High or lowUnit operation cost Low LowHigh output By batch macroproduction By massively parallel microproductionApplications Planar mechanical microparts, MEMS 3D parts, machines and mechanisms

8.1. Machining techniques

In micromechanical engineering, material working inherent

in the production of mechanical macrodevices is intendedto be used. These are mainly individual processes, such

as turning, milling, drilling, grinding, and electrochemical

machining, as well as molding, casting, punching, etc.

Batch processes are used as well.

In microelectronics-based micromechanics, batch pro-

cesses such as photolithography, etching, film deposition,

etc, are used extensively. Individual processes are avoided

since they are the bottlenecks in the course of production.

8.2. Materials in use

A wide selection of machining methods in micromechanical

engineering will allow the use of a broad spectrum of

materials, including metals and alloys, as well as polymers

and ceramics.

In microelectronics-based micromechanics silicon-

containing materials are primarily used, along with metals

and polymers that are amenable to evaporation, deposition,

and other microelectronic technologies.

8.3. Shape of components

Micromechanical engineering micromachining technologies

enable the manufacture of microparts with complex

3D geometry. Microelectronics-based technologies have

limited 3D capabilities.

8.4. Assembly methods

Assembly in micromechanical engineering is mainly

individual and includes both bonding and techniques

providing detachable and movable joints.

Attempts to avoid assembly in microelectronics-based

micromechanics constrain the choice of feasible designs.

Batch assembly by bonding has a number of drawbacks

due to the enhanced alignment accuracy required, and a

limited set of joints. In many cases individual assembly is

still needed at the final stages of batch production, and its

cost may be well above that of batch processes.

8.5. Possible designs

In microelectronics-based micromechanics, planar compo-

nents and assembly by bonding result in two basic designconcepts: planar components fitted on a horizontal base-

plate or a vertical stack of planar components.

In micromechanical engineering, 3D component shapes

and the variety of assembly techniques make possible not

only simple designs, but also sophisticated 3D machines

with movable parts.

8.6. Miniaturization and equipment precision

The limits of component miniaturization are determined by

the availability of at least several atoms of material at its

thinnest part. Thus the minimal volume of a 3D component

(micromechanical engineering) will be less than that of a

planar component (microelectronics).

To attain the limits of miniaturization, enhancement

of equipment precision is needed. Precision enhancement

of up-to-date macroequipment for batch microelectronic

technologies is a difficult task. Miniaturization of

equipment in micromechanical engineering should increase

its precision in proportion to the reduction in its size.

8.7. Process control

For batch processes, the working action cant be controlled

individually for each workpiece, and process monitoring is

performed by some representative workpiece. Therefore

the uniformity of characteristics of working action,environment, and workpieces should be ensured to obtain

identical working results for each workpiece.

Individual processes permit individual workpiece

machining feedback control using information on and

condition of both the workpiece and the working tool.

8.8. Quality control

For batch processes, quality inspection at intermediate

stages of the production cycle is carried out, at best,

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E M Kussul et al

selectively because of the individual character of inspection

operations.

Since the parts and devices in micromechanical

engineering will be mainly machined individually, it would

be possible to carry out quality inspection at intermediate

stages of production.

For monolithic devices produced by batch technologies,

defect of any component tends to make the whole device

inoperative. Under individual fabrication, a single defective

part can be replaced by an operable one.

8.9. Automation techniques

Techniques for automation of equipment, and production

processes developed for microelectronics may be applied

for the automation of batch micromechanical production.

Automation in micromechanical engineering is more

complicated, both because massively parallel individual

micromachining will require automation of a large number

of equipment units and because many of the automation

techniques from mechanical engineering have to be revised

at the microscales.

8.10. Operation cost

Miniaturization of equipment in micromechanical engineer-

ing, together with the automation of its production, will en-

able considerable reductions of cost, energy consumption,

floor area required, and labor. These should reduce the

unit cost of individual processing to the unit cost of batch

processing and below.

8.11. Volume of production

For micromechanical devices produced by batch technolo-

gies, small-lot production is not expedient because of inef-ficient use of equipment and large costs of production set-

up. Mass production of complex micromechanical devices

solely by microelectronics-based technologies also presents

a problem. Introduction of individual operations performed

by macroequipment usually leads to bottlenecks in the pro-

duction process and increases the cost of microproducts.

For micromechanical engineering, both small-lot and

mass production may be beneficial. Mass production is

achieved by the parallel operation of a large number of

pieces of microequipment.

8.12. Range of applications

The commercial potential of microelectronics-based mi-

cromechanics is for applications that require mass batch

manufacturing of planar or 2.5D parts which do not require

individual assembly, as well as for applications that require

integration with electronics (MEMS).

The range of application of micromechanical engineer-

ing should expand, through structures consisting of 3D mi-

crocomponents, microstructures demanding complicated as-

sembly and including movable parts, and for small-lot mi-

croapplications.

9. Discussion

Contemporary micromechanics has grown from microelec-

tronics and is virtually based on the technologies developed

for microelectronic devices. No other ready technology has

achieved so much success in the mass production of small

devices containing huge numbers of low-cost components

exemplified by VLSI. It is not surprising that these achieve-

ments stimulate attempts to adopt and modify microelec-

tronic technologies to the fabrication of micromechanicaldevices, however progress in this direction has been rather

slow [3, 7, 57].

We believe this is due to a great difference between

mechanical and electronic devices. This difference

manifests itself in the operating principles of these

devices, in their designs, in the requirements imposed on

materials, and in the machining and assembly methods.

In our opinion this causes a great technological difference

between micromechanics production processes and those

of microelectronics. So, it is not surprising that

commonly there is no completely ready microelectronics-

based technology for new micromechanical applications,

and that their design has to be customized to the available

technology, or a novel technology has to be developed.On the other hand, in the macroworld there exists

a lot of technology for the manufacturing of mechanical

parts and devices. For centuries, these have been

specifically developed for mechanics, but up to now their

wide use in micromechanics has not been feasible since

special microequipment for mechanical micromachining

has not been developed. We propose the successive

transfer of mechanical engineering technologies into

the microworld by smaller and smaller generations of

mechanical engineering equipment. We believe that

equipment downsizing will solve the problems of precision

and cost of mechanical micromachining.

We have also preliminarily examined a number ofpeculiarities that we consider to be characteristic of

micromechanical engineering. Some of them relate to

the necessity for changes in machine design due to

downsizing [5,27, 57, 58]. This is required to assure

operation of micromachines on their own, and in interaction

with the environment. We consider the principle of

gradual downsizing of equipment to be useful for gradual

modification of machinery design due to the problems

encountered at the microscale.

One of the most important properties of this approach

is of the possibility of supermass individual machining due

to the low cost of individual operation and the emerging

possibility of massive parallelization of machining. This

feature of massively parallel MbM looks more like thatof microelectronics, however in microelectronics such

a supermass production is provided by batch processes

that have essential restrictions from the standpoint of

mechanics. Therefore hybrid technologies combining

massively parallel MbM and batch machining may be very

promising. As an example, 2D parts could be manufactured

by batch processes, parts with complex 3D geometry

could be manufactured by parallel individual machining

using microequipment, and assembly could also be mass

individual.

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To realize the idea of massively parallel MbM,

a very high level of automation is required. It is

necessary both to realize control of miniature equipment

and to decrease the cost of human labor. One of

the problems in automation of microequipment is the

miniaturization of controllers. This problem appears

since the pace of microequipment downsizing may be

well ahead the pace of miniaturization of electronic

controllers. Solutions to this problem may be provided

by the development of non-electronic controllers thatcould become the object of micromechanical engineering

[64], as well as by feedforward automatic control

over a number of machine tools performing identical

operations using a single controller. On the other hand,

the low cost of microequipment will permit automatic

maintenance (the operation that defies automation in

macroproduction) by automatic replacement of defective or

worn microequipment.

Existing micromechanical technologies gave rise to the

market of specialized miniature devices, such as sensors,

that find application even though their cost is rather

high. The approach proposed in this paper makes it

possible to search for novel types of application due tothe potentially low cost of MbM. We consider applications

related to the development of microequipment and entire

microfactories to be very promising. Work in this area is

underway in Japan [12, 67,68]. Our approach opens the

way to a reduction in the cost of microfactories and their

transformation into personal factories for the automated

production of micromechanical devices easily available at

the price of, say, a personal computer. This, in turn, may

dramatically change the present view on the complexity and

the cost of microdevice production.

Thus the manufacturing of micromechanical devices

by miniature mechanical equipment offers a number of

advantages over batch manufacturing, and we consider it

to be a useful complement to the microelectronics-basedapproach to progress in the micromechanical field.

10. Conclusion

The approach to mechanical microdevice creation consid-

ered in this paper recommends the wide use of machining

and assembly technologies from mechanical engineering.

These technologies make it possible to fabricate mechani-

cal microdevices of sophisticated design including 3D and

movable parts with complex geometry.

To exploit mechanical engineering technologies in the

microrange, microequipment for machining and assembly

should be built up. For realization of microequipment,we propose to implement a sequence of equipment

generations with smaller and smaller dimensions. This

pathway will permit a gradual revelation and solution

of miniaturization problems, as well as developing a

spectrum of microequipment best suited for the production

of microdevices of various sizes.

Miniaturization of equipment will solve the problem

of its precision and reduce power consumption and floor

area occupied. Coupled with equipment automation, it

will drastically reduce the cost of microequipment and

microdevices produced, especially for mass production. In

such a way, the range of cost-effective micromechanical

applications is supposed to be extended through a

widening of the scope of feasible microdesigns and

low-cost manufacturing and assembly of mechanical

microcomponents.

Acknowledgments

The authors would like to thank Jiri Soukup for valuable

comments, Fred Runyan and Tanya Olar for their help

and suggestions, Toshio Fukuda and Naomi Akao for

providing the most useful Proceedings of the International

Symposiums on Micro Machine and Human Science.

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